Permanent Magnet Selection and Design Considerations for Traction Motors Using Dynamic Demagnetization Analysis

The demand for electrical vehicles has been fueled as an alternative to the conventional engine vehicles in view of emission free transportation and depletion of natural oil resources. Interior permanent magnet synchronous motors are considered as good choice for the electric vehicle propulsion system due to unique advantages such as high efficiency, power to weight ratio and extended speed ranges. The permanent magnets present in the traction motor are prone to irreversible demagnetization due to negative d-axis currents resulting from regular operation or Active short circuit or Freewheeling operations. The selection of permanent magnets for traction motor application plays vital role in the vehicle performance and functional safety aspects. This paper addresses the permanent magnet demagnetization and choice of permanent magnet manufacturing technology in initial design stage. The dynamic demagnetization analysis is carried out using FEA based Maxwell 2D electromagnetics software.